The present invention relates to a vacuum blood sample collecting device for collecting a blood sample in a blood container.
One known vacuum blood sample collecting device is disclosed in Japanese Patent Publication No. 51-3153. The disclosed vacuum blood sampler has a blood container disposed in a vacuum blood sampling chamber which is evacuated by a vacuum pump. The vacuum pump develops a vacuum that acts in the blood container to produce a suction force in a blood sampling needle connected to the blood container through a tube or the like for thereby drawing blood from a blood vessel in a blood donor or patient. The vacuum or negative pressure after the blood starts being sampled is required to be kept at a suitable level for facilitating the blood sampling operation and reducing the burden on the blood donor. To regulate the pressure in the vacuum blood sampling chamber to an adequate level, a pressure regulating valve is disposed in a vacuum pipe which interconnects the vacuum pump and the vacuum blood sampling chamber. When the pressure in the vacuum blood sampling chamber reaches a desired target level, a spring-loaded leakage mechanism in the pressure regulating valve is operated to keep the pressure in the vacuum blood sampling chamber at the target level.
With the above prior arrangement, even after the pressure in the vacuum blood sampling chamber has reached the target level, the vacuum pump is continuously operated. Therefore, the vacuum blood sampler is of poor electric efficiency and generates heat. During operation of the vacuum blood sampler over a relatively long period of time, the seals and spring of the leakage mechanism in the pressure regulating valve are deteriorated to vary a control pressure, thus making it difficult to maintain the desired target pressure in the vacuum blood sampling chamber. The desired target pressure cannot easily be varied and set since it is controlled by a skilled operator through adjustment of the resiliency of the spring of the leakage mechanism.
When the vacuum level is quickly lowered toward a final target level, the force tending to draw blood from the blood vessel is rapidly varied to put an excessive burden on the blood donor, and a blood vessel wall is attracted to the blood sampling needle under the large suction force developed in the hole of the blood sampling needle. If the blood vessel in the blood donor is narrower than normal, the needle hole may be closed by the blood vessel wall, making it difficult or impossible to effect continued blood sampling operation. Accordingly, the efficiency of blood sampling is lowered.